Acrylic pressure-sensitive adhesives with acylaziridine crosslinking agents

ABSTRACT

A pre-adhesive composition is described comprising an acid-functional (meth)acrylate copolymer and an acylaziridine crosslinking agent, which when crosslinked provides a pressure-sensitive adhesive and pressure-sensitive adhesive articles.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. application Ser. No.12/547,008, filed Aug. 25, 2009, now allowed, the disclosure of which isincorporated by reference in their entirety herein.

TECHNICAL FIELD OF THE INVENTION

This invention relates to pressure-sensitive adhesives and tape articlesprepared therefrom. The tapes are characterized by exhibiting an overallbalance of adhesive and cohesive characteristics and exceptional loadbearing capabilities at elevated temperatures.

BACKGROUND OF THE INVENTION

Pressure-sensitive tapes are virtually ubiquitous in the home andworkplace. In its simplest configuration, a pressure-sensitive tapecomprises an adhesive and a backing, and the overall construction istacky at the use temperature and adheres to a variety of substratesusing only moderate pressure to form the bond. In this fashion,pressure-sensitive tapes constitute a complete, self-contained bondingsystem.

According to the Pressure-Sensitive Tape Council, pressure-sensitiveadhesives (PSAs) are known to possess properties including thefollowing: (1) aggressive and permanent tack, (2) adherence with no morethan finger pressure, (3) sufficient ability to hold onto an adherend,and (4) sufficient cohesive strength to be removed cleanly from theadherend. Materials that have been found to function well as PSAsinclude polymers designed and formulated to exhibit the requisiteviscoelastic properties resulting in a desired balance of tack, peeladhesion, and shear holding power. PSAs are characterized by beingnormally tacky at room temperature (e.g., 20° C.). PSAs do not embracecompositions merely because they are sticky or adhere to a surface.

These requirements are assessed generally by means of tests which aredesigned to individually measure tack, adhesion (peel strength), andcohesion (shear holding power), as noted in A.V. Pocius in Adhesion andAdhesives Technology: An Introduction, 2^(nd) Ed., Hanser GardnerPublication, Cincinnati, Ohio, 2002. These measurements taken togetherconstitute the balance of properties often used to characterize a PSA.

With broadened use of pressure-sensitive tapes over the years,performance requirements have become more demanding. Shear holdingcapability, for example, which originally was intended for applicationssupporting modest loads at room temperature, has now increasedsubstantially for many applications in terms of operating temperatureand load. So-called high performance pressure-sensitive tapes are thosecapable of supporting loads at elevated temperatures for 10,000 minutes.Increased shear holding capability has generally been accomplished bycrosslinking the PSA, although considerable care must be exercised sothat high levels of tack and adhesion are retained in order to retainthe aforementioned balance of properties.

There are two major crosslinking mechanisms for acrylic adhesives:free-radical copolymerization of multifunctional ethylenicallyunsaturated groups with the other monomers, and covalent or ioniccrosslinking through the functional monomers, such as acrylic acid.Another method is the use of UV crosslinkers, such as copolymerizablebenzophenones or post-added photocrosslinkers, such as multifunctionalbenzophenones and triazines. In the past, a variety of differentmaterials have been used as crosslinking agents, e.g., polyfunctionalacrylates, acetophenones, benzophenones, and triazines. The foregoingcrosslinking agents, however, possess certain drawbacks which includeone or more of the following: high volatility; incompatibility withcertain polymer systems; generation of corrosive or toxic by-products;generation of undesirable color; requirement of a separate photoactivecompound to initiate the crosslinking reaction; and high sensitivity tooxygen.

SUMMARY

Briefly, the present disclosure provides a pre-adhesive, curablecomposition comprising an acid-functional (meth)acrylate copolymer andan acylaziridine crosslinking agent, which when crosslinked provides apressure-sensitive adhesive composition. In one aspect, the disclosureprovides a novel pre-adhesive syrup polymer composition comprising a) afirst component acid-functional (meth)acrylate solute copolymer, b) asecond component comprising at least one free-radically polymerizablesolvent monomer, and c) an acylaziridine crosslinking agent. Thepre-adhesive syrup polymer composition may be polymerized andcrosslinked to produce a pressure-sensitive adhesive.

In another embodiment the disclosure provides an adhesive emulsioncomprising an aqueous emulsion of the acid-functional (meth)acrylatecopolymer, and the acylaziridine crosslinking agent which may be coatedand crosslinked to form a pressure-sensitive adhesive. In a relatedembodiment, the present disclosure provides an adhesive emulsioncomprising an aqueous emulsion of the reaction product of theacid-functional (meth)acrylate copolymer, and the acylaziridinecrosslinking agent which may be coated and cured to form apressure-sensitive adhesive.

For environmental reasons, there is a desire to move away from the useof volatile organic solvents (VOC's) in coating processes, and towardsmore environmentally friendly water-based materials, so the presentinvention provides a waterborne adhesive comprising an aqueous emulsionsupra. Waterborne systems are desirable for cost, environmental, safety,and regulatory reasons. The aqueous system may be readily coated, andprovides a pressure-sensitive adhesive when cured.

The pressure-sensitive adhesives, the crosslinked compositions, of thisdisclosure provide the desired balance of tack, peel adhesion, and shearholding power, and further conform to the Dahlquist criteria; i.e. themodulus of the adhesive at the application temperature, typically roomtemperature, is less than 3×10⁶ dynes/cm at a frequency of 1 Hz.

The use of the acyl aziridine crosslinking agent affords a number ofadvantages as compared to the use of conventional crosslinking agentsfor (meth)acrylic adhesives. These advantages include, but are notlimited to, decreased sensitivity of the crosslinkable composition tooxygen; the avoidance of evolution of any toxic or corrosive by-productsor discoloration of the final product; and the capability to be used asa post-curing crosslinking additive. Furthermore, the crosslinkingagents have the following advantages over previously described agents:ease of synthesis, high solubility in the component monomers or organicsolvents, and low cost starting materials.

In some embodiments, this disclosure provides an adhesive compositionderived from renewable resources. In particular, the present inventionprovides an adhesive composition derived, in part, from plant materials.In some embodiments, the present invention further provides an adhesivearticle, wherein the substrate or backing is also derived from renewableresources. The increase in the price of oil, and concomitantpetroleum-derived products, has led to volatile prices and supply formany adhesive products. It is desirable to replace all or part of thepetroleum-based feedstocks with those derived from renewable sources,such as plants, as such materials become relatively cheaper, and aretherefore both economically and socially beneficial. Therefore, the needfor such plant-derived materials has become increasingly significant.

In this application “pre-adhesive” refers to the solution, suspension,or emulsion comprising an acid-functional (meth)acrylate copolymer, andan acylaziridine crosslinking agent which may be crosslinked to form apressure-sensitive adhesive.

“Syrup polymer” refers to a solution of a solute polymer in one or moresolvent monomers, the solution having a viscosity of from 500 to 10,000cPs at 22° C. “Solution polymer” refers to a solution of a solutepolymer in one or more organic solvents.

In this application, (meth)acrylic is inclusive of both methacrylic andacrylic.

As used herein, “alkyl” includes straight-chained, branched, and cyclicalkyl groups and includes both unsubstituted and substituted alkylgroups. Unless otherwise indicated, the alkyl groups typically containfrom 1 to 20 carbon atoms. Examples of “alkyl” as used herein include,but are not limited to, methyl, ethyl, n-propyl, n-butyl, n-pentyl,isobutyl, t-butyl, isopropyl, n-octyl, n-heptyl, ethylhexyl,cyclopentyl, cyclohexyl, cycloheptyl, adamantyl, and norbornyl, and thelike. Unless otherwise noted, alkyl groups may be mono- or polyvalent.

As used herein, the term “heteroalkyl” includes both straight-chained,branched, and cyclic alkyl groups with one or more heteroatomsindependently selected from S, O, and N with both unsubstituted andsubstituted alkyl groups. Unless otherwise indicated, the heteroalkylgroups typically contain from 1 to 20 carbon atoms. “Heteroalkyl” is asubset of “hydrocarbyl containing one or more S, N, O, P, or Si atoms”described below. Examples of “heteroalkyl” as used herein include, butare not limited to, methoxy, ethoxy, propoxy, 3,6-dioxaheptyl,3-(trimethylsilyl)-propyl, 4-dimethylaminobutyl, and the like. Unlessotherwise noted, heteroalkyl groups may be mono- or polyvalent.

As used herein, “aryl” is an aromatic group containing 6-18 ring atomsand can contain optional fused rings, which may be saturated,unsaturated, or aromatic. Examples of an aryl groups include phenyl,naphthyl, biphenyl, phenanthryl, and anthracyl. Heteroaryl is arylcontaining 1-3 heteroatoms such as nitrogen, oxygen, or sulfur and cancontain fused rings. Some examples of heteroaryl groups are pyridyl,furanyl, pyrrolyl, thienyl, thiazolyl, oxazolyl, imidazolyl, indolyl,benzofuranyl, and benzthiazolyl. Unless otherwise noted, aryl andheteroaryl groups may be mono- or polyvalent.

As used herein, “(hetero)hydrocarbyl” is inclusive of hydrocarbyl alkyland aryl groups, and heterohydrocarbyl heteroalkyl and heteroarylgroups, the later comprising one or more catenary oxygen heteroatomssuch as ether or amino groups. Heterohydrocarbyl may optionally containone or more catenary (in-chain) functional groups including ester,amide, urea, urethane, and carbonate functional groups. Unless otherwiseindicated, the non-polymeric (hetero)hydrocarbyl groups typicallycontain from 1 to 60 carbon atoms. Some examples of suchheterohydrocarbyls as used herein include, but are not limited to,methoxy, ethoxy, propoxy, 4-diphenylaminobutyl,2-(2′-phenoxyethoxy)ethyl, 3,6-dioxaheptyl, 3,6-dioxahexyl-6-phenyl, inaddition to those described for “alkyl”, “heteroalkyl”, “aryl”, and“heteroaryl” supra.

DETAILED DESCRIPTION

The present disclosure provides a pre-adhesive composition comprising anacid-functional (meth)acrylate copolymer and an acylaziridinecrosslinking agent, which when crosslinked, provides apressure-sensitive adhesive and pressure-sensitive adhesive articles.

The (meth)acrylate ester monomer useful in preparing the acid functional(meth)acrylate adhesive copolymer is a monomeric (meth)acrylic ester ofa non-tertiary alcohol, which alcohol contains from 1 to 14 carbon atomsand preferably an average of from 4 to 12 carbon atoms.

Examples of monomers suitable for use as the (meth)acrylate estermonomer include the esters of either acrylic acid or methacrylic acidwith non-tertiary alcohols such as ethanol, 1-propanol, 2-propanol,1-butanol, 2-butanol, 1-pentanol, 2-pentanol, 3-pentanol,2-methyl-1-butanol, 3-methyl-1-butanol, 1-hexanol, 2-hexanol,2-methyl-1-pentanol, 3-methyl-1-pentanol, 2-ethyl-1-butanol,3,5,5-trimethyl-1-hexanol, 3-heptanol, 1-octanol, 2-octanol,isooctylalcohol, 2-ethyl-1-hexanol, 1-decanol, 2-propylheptanol,1-dodecanol, 1-tridecanol, 1-tetradecanol, citronellol,dihydrocitronellol, and the like. In some embodiments, the preferred(meth)acrylate ester monomer is the ester of (meth)acrylic acid withbutyl alcohol or isooctyl alcohol, or a combination thereof, althoughcombinations of two or more different (meth)acrylate ester monomer aresuitable. In some embodiments, the preferred (meth)acrylate estermonomer is the ester of (meth)acrylic acid with an alcohol derived froma renewable source, such as 2-octanol, citronellol, dihydrocitronellol.

In some embodiments it is desirable for the (meth)acrylic acid estermonomer to include a high T_(g) monomer, have a T_(g) of at least 25°C., and preferably at least 50° C. Suitable high Tg monomers includeExamples of suitable monomers useful in the present invention include,but are not limited to, t-butyl acrylate, methyl methacrylate, ethylmethacrylate, isopropyl methacrylate, n-butyl methacrylate, isobutylmethacrylate, s-butyl methacrylate, t-butyl methacrylate, stearylmethacrylate, phenyl methacrylate, cyclohexyl methacrylate, isobornylacrylate, isobornyl methacrylate, benzyl methacrylate, 3,3,5trimethylcyclohexyl acrylate, cyclohexyl acrylate, N-octyl acrylamide,and propyl methacrylate or combinations.

The (meth)acrylate ester monomer is present in an amount of 85 to 99.5parts by weight based on 100 parts total monomer content used to preparethe polymer. Preferably (meth)acrylate ester monomer is present in anamount of 90 to 95 parts by weight based on 100 parts total monomercontent. When high Tg monomers are included, the copolymer may includeup to 30 parts by weight, preferably up to 20 parts by weight of the 85to 99.5 parts by weight of (meth)acrylate ester monomer component. Insuch embodiments, the copolymer may comprise:

-   -   i. 55 to 69.5 parts by weight of an (meth)acrylic acid ester of        non-tertiary alcohol;    -   ii. 1 to 30 parts by weight of an (meth)acrylic acid ester        having a T_(g) of greater than 25° C.;    -   iii. 0.5 to 15 parts by weight of an acid functional        ethylenically unsaturated monomer;    -   iv. 0 to 10 parts by weight of a non-acid functional,        ethylenically unsaturated polar monomer;    -   v. 0 to 5 parts vinyl monomer; and    -   vi. 0 to 5 parts of a multifunctional (meth)acrylate;    -   based on 100 parts by weight total monomer.

The polymer further comprises an acid functional monomer, where the acidfunctional group may be an acid per se, such as a carboxylic acid, or aportion may be salt thereof, such as an alkali metal carboxylate. Usefulacid functional monomers include, but are not limited to, those selectedfrom ethylenically unsaturated carboxylic acids, ethylenicallyunsaturated sulfonic acids, ethylenically unsaturated phosphonic acids,and mixtures thereof. Examples of such compounds include those selectedfrom acrylic acid, methacrylic acid, itaconic acid, fumaric acid,crotonic acid, citraconic acid, maleic acid, oleic acid, β-carboxyethyl(meth)acrylate, 2-sulfoethyl methacrylate, styrene sulfonic acid,2-acrylamido-2-methylpropanesulfonic acid, vinylphosphonic acid, andmixtures thereof.

Due to their availability, acid functional monomers of the acidfunctional copolymer are generally selected from ethylenicallyunsaturated carboxylic acids, i.e. (meth)acrylic acids. When evenstronger acids are desired, acidic monomers include the ethylenicallyunsaturated sulfonic acids and ethylenically unsaturated phosphonicacids. The acid functional monomer is generally used in amounts of 0.5to 15 parts by weight, preferably 0.5 to 10 parts by weight, based on100 parts by weight total monomer.

The polar monomers useful in preparing the copolymer are both somewhatoil soluble and water soluble, resulting in a distribution of the polarmonomer between the aqueous and oil phases in an emulsionpolymerization. As used herein the term “polar monomers” are exclusiveof acid functional monomers.

Representative examples of suitable polar monomers include but are notlimited to 2-hydroxyethyl (meth)acrylate; N-vinylpyrrolidone;N-vinylcaprolactam; acrylamide; mono- or di-N-alkyl substitutedacrylamide; t-butyl acrylamide; dimethylaminoethyl acrylamide; N-octylacrylamide; poly(alkoxyalkyl) (meth)acrylates including2-(2-ethoxyethoxy)ethyl (meth)acrylate, 2-ethoxyethyl (meth)acrylate,2-methoxyethoxyethyl (meth)acrylate, 2-methoxyethyl methacrylate,polyethylene glycol mono(meth)acrylates; alkyl vinyl ethers, includingvinyl methyl ether; and mixtures thereof. Preferred polar monomersinclude those selected from the group consisting of 2-hydroxyethyl(meth)acrylate and N-vinylpyrrolidinone. The polar monomer may bepresent in amounts of 0 to 10 parts by weight, preferably 0.5 to 5 partsby weight, based on 100 parts by weight total monomer.

When used, vinyl monomers useful in the (meth)acrylate polymer includevinyl esters (e.g., vinyl acetate and vinyl propionate), styrene,substituted styrene (e.g., α-methyl styrene), vinyl halide, and mixturesthereof. As used herein vinyl monomers are exclusive of acid functionalmonomers, acrylate ester monomers and polar monomers. Such vinylmonomers are generally used at 0 to 5 parts by weight, preferably 1 to 5parts by weight, based on 100 parts by weight total monomer.

In order to increase cohesive strength of the coated adhesivecomposition, a multifunctional (meth)acrylate may be incorporated intothe blend of polymerizable monomers. Multifunctional acrylates areparticularly useful for emulsion or syrup polymerization. Examples ofuseful multifunctional (meth)acrylate include, but are not limited to,di(meth)acrylates, tri(meth)acrylates, and tetra(meth)acrylates, such as1,6-hexanediol di(meth)acrylate, poly(ethylene glycol)di(meth)acrylates, polybutadiene di(meth)acrylate, polyurethanedi(meth)acrylates, and propoxylated glycerin tri(meth)acrylate, andmixtures thereof. The amount and identity of multifunctional(meth)acrylate is tailored depending upon application of the adhesivecomposition. Typically, the multifunctional (meth)acrylate is present inamounts less than 5 parts based on total dry weight of adhesivecomposition. More specifically, the crosslinker may be present inamounts from 0.01 to 5 parts, preferably 0.05 to 1 parts, based on 100parts total monomers of the adhesive composition.

The adhesive composition further comprises an acylaziridine crosslinkingagent, in addition to the (meth)acrylate copolymer. The acylaziridinecrosslinking agent is generally added in amounts of 0.005 to 5.0 partsby weight of an acylaziridine crosslinking agent, relative to 100 partsof the copolymer.

The acylaziridine crosslinking agent is of the general formula:

wherein

R¹ is H or CH₃; X¹ is —O— or —NH—;

R² is a (hetero)hydrocarbyl group,

X² is —O— or —NH—;

x is 0 or 1;each R³ is independently —H or a C₁-C₄ alkyl group,y is 0, 1 or 2.

In one method, the acylaziridine crosslinking agent may be prepared byacylation of an aziridine compound as shown in Scheme 1.

wherein R¹, X¹, R², X², x, R³, and y are as previously defined forFormula I, and X³ is an alkoxy group or a halide.

The hydroxyacid precursor to the acylaziridine of Formula I can be anyhydroxyacid, e.g., a hydroxycarboxylic acid, or the correspondinglactone or ester. Suitable hydroxycarboxylic acids include(hetero)hydrocarbyl hydroxyalkyl carboxylic acids including alkylene,arylene, alkarylene, aralkylene, heteroalkylene and heteroarylene.Useful alkylene hydroxyacids include hydroxyacetic acid,hydroxypropionic acids (e.g., 2- or 3-hydroxypropionic acid),hydroxybutyric acids (e.g., 2-, 3-, or 4-hydroxybutyric acid),hydroxyvaleric acids (e.g. 2-, 3- 4-, or 5-hydroxyvaleric acid),hydroxycaproic acids (e.g., 2-, 3-, 4-, 5-, or 6-hydroxycaproic acid),branched chain hydroxyalkyl carboxylic acids (e.g.2-hydroxydimethylacetic acid), malic acid monoesters, and the like.Suitable lactones include lactides, 1,4-dioxanone, valerolactone, andcaprolactone. Suitable cyclic carbonates include trimethylene carbonate.

In some embodiments R² is a straight or branched chain alkylenepreferably containing from one to about six carbon atoms. When R² isalkylene it can also contain hetero functional groups such as carbonyl,oxy, or catenary nitrogen, preferably fully substituted catenarynitrogen wherein the substituent is free of hydrogen-donor hydrogenbonding functional groups. In another embodiment R² can be arylene(e.g., 1,4-phenylene) or arylene substituted by lower alkyl or loweralkoxy R² can also be a combination of such arylene, alkenylene, andalkylene groups, such as 1,4-xylylene.

As can be see in Scheme 1, the acylaziridine of formula I may be derivedfrom an acylated compound of the formula:

This in turn may be derived from precursor amino acid (or functionalequivalent thereof) which can be any compound having an amino group,preferably a primary amino group, at least one carbon atom removed froman acid group such as a carboxylic acid group. Exemplary amino acidsinclude primary or secondary amino acids such as sarcosine and proline.

Alternatively, the acylaziridine compounds of Formula I may be preparedas shown in Scheme 2.

wherein R¹, X¹, R², X², x, R³, and y are as previously defined forFormula I, and X³ is an alkoxy group or a halide.

Compounds of Formula I where X² is NH and x is 1 may be prepared by thereaction of an aziridine compound with an acrylated isocyanate as shownin Scheme 3.

wherein R¹, X¹, R², R³, and y are as previously defined for Formula I.

Useful precursor isocyanato (meth)acryloyl compounds include2-isocyanatoethyl (meth)acrylate, 3-isocyanatopropyl (meth)acrylate,2-acrylamidoethylisocyanate, 3-acrylamidopropylisocyanate,3-methacrylamidopropylisocyanate, 4-methacryloyloxycyclohexylisocyanate,and 5-acryloyloxymethyl-3,3,5-trimethylcyclohexylisocyanate.

In some embodiments, compounds of Formula I, where X¹ is NH and y is 0may be prepared by the reaction of an aziridine with a vinyl azlactoneas shown in Scheme 4. Useful azlactone precursor compounds are describedin U.S. Pat. No. 7,304,112 (Lewandowski et al.), incorporated herein byreference.

wherein R³ and y are as previously defined for Formula I.

In another embodiment, compound of Formula I may be prepared from thereaction product of a hydroxy- or aminoalkyl acrylate and a diacid (orfunctional equivalent, such as an ester), followed by an aziridinecompound as shown in Scheme 5:

wherein

R¹ is H or CH₃;

Each X¹, and X⁴ is independently —O— or —NH—;Each R⁴ and R⁵ is independently a (hetero)hydrocarbyl group,X³ is an alkoxy group or a halide. Preferably R⁴ and R⁵ are eachselected from alkylene or arylene groups. Most preferably, R⁴ and R⁵ areselected from alkylene groups.

As can be seen, the monoacryloyl compound is derived from a diol ordiamine. Useful monoacrylates include the mono (meth)acrylic acid esterof aliphatic diols such as ethyleneglycol, triethyleneglycol,2,2-dimethyl-1,3-propanediol, 1,3-cyclopentanediol,1-ethoxy-2,3-propanediol, 2-methyl-2,4-pentanediol, 1,4-cyclohexanediol,1,6-hexamethylenediol, 1,2-cyclohexanediol, 1,6-cyclohexanedimethanol;the mono (meth)ylacrylic acid esters of aromatic diols such asresorcinol, pyrocatechol, bisphenol-A, and bis(2-hydroxyethyl)phthalate; the monoacrylic acid ester of aromatic triols such aspyrogallol, phloroglucinol, and 2-phenyl-2,2-methylolethanol. Themonoacryloyl compounds may also be derived from the correspondingdiamines.

Useful diacids in the above reaction scheme include oxalic acid, malonicacid, succinic acid, glutaric acid, adipic acid, 1,12 dicarboxydodecane,fumaric acid, and maleic acid phthalic acid, isophthalic acid andterephthalic acid.

The acylaziridine crosslinking agent may be copolymerized with themonomers of the acid functional (meth)acrylate copolymer, or may beadded to the extant copolymer. It is believed that the acylaziridinegroup reacts with the pendent acid functional groups of the acidfunctional (meth)acrylate copolymer to form a carboxyethyleneaminolinkage. In one embodiment, where the acylaziridine is added to theextant polymer, the intermediate may be of the following structure, withthe optional monomer units and unreacted (free) acid functional monomerunits not shown. The pendent (meth)acrylate group may be subsequentlyfree radically polymerized to crosslink the copolymer. With respect tothe R³ group, it will be understood that it may be attached to thecarbon adjacent to the —NH-group as depicted, or attached to the carbonadjacent the —O—, depending on the ring-opening.

whereM_(acrylate) represents polymerized monomer units derived from(meth)acrylate monomers,M_(acid) represents polymerized monomer units derived from acidfunctional monomers, a and b are at least one;a and b are each at least one, and R¹, X¹, R², X², x, R³, and y are aspreviously defined for Formula I. It will be understood that a and b maybe of values corresponding to the amounts of the monomers in thepolymerizable composition, i.e. 85 to 99.5 parts by weight of an(meth)acrylic acid ester monomer; and 0.5 to 15 parts by weight of anacid functional monomer. Although not depicted in Formula II, othermonomers may be present in the amounts previously recited.

In another embodiment, the acyl aziridine is copolymerized with theother monomers to produce a copolymer having a pendent acylaziridinegroup. This pendent group may subsequently react with an acid group,resulting in ring-opening of the aziridine ring, and crosslinking of thecopolymers as shown in Scheme 6.

whereM_(acrylate) represents polymerized monomer units derived from(meth)acrylate monomers,M_(acid) represents polymerized monomer units derived from acidfunctional monomers,M_(azir) represents polymerized monomer units derived from theacylaziridine of Formula I;a, b and c are at least one;and R¹, X¹, R², X², x, R³, and y are as previously defined for FormulaI. It will be understood that a, b and c may be of values correspondingto the amounts of the monomers in the polymerizable composition, i.e. 85to 99.5 parts by weight of an (meth)acrylic acid ester monomer; 0.5 to15 parts by weight of an acid functional monomer, and 0.005 to 5.0 partsby weight of the acylaziridine crosslinking agent. Although not depictedin Scheme 6, other monomers may be present in the amounts previouslyrecited.

The acid functional copolymers can be prepared by any conventional freeradical polymerization method, including solution, radiation, bulk,dispersion, emulsion, and suspension processes. The (meth)acrylatepolymers may be prepared via suspension polymerizations as disclosed inU.S. Pat. Nos. 3,691,140 (Silver); 4,166,152 (Baker et al.); 4,636,432(Shibano et al); 4,656,218 (Kinoshita); and 5,045,569 (Delgado). Eachdescribes adhesive compositions, and the descriptions of polymerizationprocesses are incorporated herein by reference.

Water-soluble and oil-soluble initiators useful in preparing the acidfunctional copolymers are initiators that, on exposure to heat, generatefree-radicals which initiate (co)polymerization of the monomer mixture.Water-soluble initiators are preferred for preparing the (meth)acrylatepolymers by emulsion polymerization. When used, initiators may comprisefrom about 0.05 to about 1 part by weight, preferably about 0.1 to about0.5 part by weight based on 100 parts by weight of monomer components inthe acid functional copolymers.

Suitable water-soluble initiators include but are not limited to thoseselected from the group consisting of potassium persulfate, ammoniumpersulfate, sodium persulfate, and mixtures thereof; oxidation-reductioninitiators such as the reaction product of the above-mentionedpersulfates and reducing agents such as those selected from the groupconsisting of sodium metabisulfite and sodium bisulfate; and4,4′-azobis(4-cyanopentanoic acid) and its soluble salts (e.g., sodium,potassium). The preferred water-soluble initiator is potassiumpersulfate. Suitable oil-soluble initiators include but are not limitedto those selected from the group consisting of azo compounds such asVAZO™ 64 (2,2′-azobis(isobutyronitrile)), VAZO™ 67 (2,2′ azobis(2-methylbutyronitrile)), and VAZO™ 52(2,2′-azobis(2,4-dimethylpentanenitrile)), available from E.I. du Pontde Nemours Co., peroxides such as benzoyl peroxide and lauroyl peroxide,and mixtures thereof. The preferred oil-soluble thermal initiator is2,2′-azobis-(2,4-dimethylpentanenitrile).

The copolymerizable emulsion mixture may optionally further comprisechain transfer agents to control the molecular weight of the resultantpolymer. Examples of useful chain transfer agents include but are notlimited to those selected from the group consisting of carbontetrabromide, alcohols, mercaptans, and mixtures thereof. When present,the preferred chain transfer agents are isooctylthioglycolate and carbontetrabromide. The emulsion mixture may further comprise up to about 0.5parts by weight of a chain transfer agent, typically about 0.01 to about0.5 parts by weight, if used, preferably about 0.05 parts by weight toabout 0.2 parts by weight, based upon 100 parts by weight of the totalmonomer mixture.

Polymerization of the acid functional copolymers via emulsion techniquesmay require the presence of an emulsifier (which may also be called anemulsifying agent or a surfactant). Useful emulsifiers for the presentinvention include those selected from the group consisting of anionicsurfactants, cationic surfactants, nonionic surfactants, and mixturesthereof.

Preferably, emulsion polymerization is carried out in the presence ofanionic surfactant(s). A useful range of emulsifier concentration isfrom about 0.5 to about 8 weight percent, preferably from about 1 toabout 5 weight percent, based on the total weight of all monomers of theemulsion pressure-sensitive adhesive.

The acid functional (meth)acrylate copolymers may be prepared by abatch, continuous or semi-continuous emulsion polymerization process.The polymerization generally comprises the steps of:

(a) making a monomer premix comprising;

-   -   (i) a (meth)acrylic acid ester monomer,    -   (ii) an acid functional monomer;    -   (iii) optionally a polar monomer,    -   (iv) optionally a vinyl monomer,    -   (v) optionally a multifunctional (meth)acrylate;    -   (vi) optionally a chain transfer agent,

(b) combining said premix with a water phase comprising:

-   -   (i) water,    -   (ii) a surfactant selected from the group consisting of anionic        surfactants, nonionic surfactants, cationic surfactants,        amphoteric surfactants, polymeric surfactants, and mixtures        thereof,    -   (iii) a free radical initiator, preferable a water soluble        initiator,

(c) concurrently agitating and heating said emulsion to a temperature ofabout 30° C. to about 80° C., and permitting polymerization of saidmonomers in the oil-in-water emulsion until a polymeric latex is formed.It will be understood that other mixtures may be used. For example, theacid functional monomer, or other hydrophilic monomers, may be added tothe aqueous solution. In addition, once the emulsion mixture isprepared, the monomers may partition between the oil phase and the waterphase, according to their respective partition coefficients. It will beunderstood that the monomer premix may also include the acyl aziridine.Alternatively, the acyl aziridine may be added to the extant polymer.

A neutralizing agent may be employed in the preparation of thiscopolymer. It may be employed at a level sufficient to neutralize all ora part of the acid groups of the polymer. Neutralization is achieved viathe use of an alkali metal hydroxide or a combination of an alkali metalhydroxide with a minor amount of another neutralizing agent. A widevariety of other neutralizing agents may be used as will be understoodby those skilled in the art. The selection of the other neutralizingagent, and the amount employed may be varied to achieve a desiredresult. However, the type and amount selected must not render theadhesive non-dispersible. Preferably ammonium, sodium and potassiumhydroxide are used as neutralizing agents.

An alternate method of preparing acid functional (meth)acrylatecopolymers comprises partially polymerizing monomers to produce a syruppolymer comprising the acid functional (meth)acrylate copolymer andunpolymerized monomers. The syrup polymer composition is polymerized toa useful coating viscosity, which may be coated onto a substrate (suchas a tape backing) and further polymerized. Partial polymerizationprovides a coatable solution of the acid functional (meth)acrylatesolute copolymer in one or more solvent monomers. Generally, theacylaziridine crosslinking agent is added to the partially polymerizedcomposition, then coated on a suitable substrate and furtherpolymerized. In an alternate embodiment, the acylaziridine crosslinkingagent is added to the mixture of polymerizable monomers, and partiallypolymerized as previously described.

For syrup application processing, a preferred monomer mixture (secondcomponent) comprises 85 to 99.5 pbw of one or more (meth)acrylate estermonomers, 0.5 to 15 pbw of acid functional monomers, 0 to 10 pbw of oneor more second, non-acid, polar monomers, and 0 to about 5 pbw of othervinyl monomers, based on 100 parts total monomer. It will be understoodthat the monomer mix may also include the acyl aziridine. Alternatively,the acyl aziridine may be added to the extant polymer.

The polymerizations may be conducted in the presence of, or preferablyin the absence of, suitable solvents such as ethyl acetate, toluene andtetrahydrofuran which are unreactive with the functional groups of thecomponents of the syrup polymer.

Polymerization can be accomplished by exposing the syrup polymercomposition to energy in the presence of a photoinitiator. Energyactivated initiators may be unnecessary where, for example, ionizingradiation is used to initiate polymerization. These photoinitiators canbe employed in concentrations ranging from about 0.0001 to about 3.0pbw, preferably from about 0.001 to about 1.0 pbw, and more preferablyfrom about 0.005 to about 0.5 pbw, per 100 pbw of the solventmonomer(s).

A preferred method of preparation of the syrup polymer is photoinitiatedfree radical polymerization. Advantages of the photopolymerizationmethod are that 1) heating the monomer solution is unnecessary and 2)photoinitiation is stopped completely when the activating light sourceis turned off. Polymerization to achieve a coatable viscosity may beconducted such that the conversion of monomers to polymer is up to about30%. Polymerization can be terminated when the desired conversion andviscosity have been achieved by removing the light source and bybubbling air (oxygen) into the solution to quench propagating freeradicals. The solute polymer(s) may be prepared conventionally in anon-monomeric solvent and advanced to high conversion (degree ofpolymerization). When solvent (monomeric or non-monomeric) is used, thesolvent may be removed (for example by vacuum distillation) eitherbefore or after formation of the syrup polymer. While an acceptablemethod, this procedure involving a highly converted functional polymeris not preferred because an additional solvent removal step is required,another material may be required (the non-monomeric solvent), anddissolution of the high molecular weight, highly converted solutepolymer in the monomer mixture may require a significant period of time.

Useful photoinitiators include benzoin ethers such as benzoin methylether and benzoin isopropyl ether; substituted acetophenones such as2,2-dimethoxyacetophenone, available as Irgacure™ 651 photoinitiator(Ciba Specialty Chemicals), 2,2 dimethoxy-2-phenyl-1-phenylethanone,available as Esacure™ KB-1 photoinitiator (Sartomer Co.; West Chester,Pa.), and dimethoxyhydroxyacetophenone; substituted α-ketols such as2-methyl-2-hydroxy propiophenone; aromatic sulfonyl chlorides such as2-naphthalene-sulfonyl chloride; and photoactive oximes such as1-phenyl-1,2-propanedione-2-(O-ethoxy-carbonyl)oxime. Particularlypreferred among these are the substituted acetophenones.

Preferred photoinitiators are photoactive compounds that undergo aNorrish I cleavage to generate free radicals that can initiate byaddition to the acrylic double bonds. The photoinitiator can be added tothe mixture to be coated after the copolymer has been formed, i.e.,photoinitiator can be added to the syrup polymer mixture. Suchpolymerizable photoinitiators are described, for example, in U.S. Pat.Nos. 5,902,836 and 5,506,279 (Babu et al.).

The syrup polymer composition and the photoinitiator may be irradiatedwith activating UV radiation to polymerize the monomer component(s). UVlight sources can be of two types: 1) relatively low light intensitysources such as Blacklights which provide generally 10 mW/cm² or less(as measured in accordance with procedures approved by the United StatesNational Institute of Standards and Technology as, for example, with aUVIMAP™ UM 365 L-S radiometer manufactured by Electronic Instrumentation& Technology, Inc., in Sterling, Va.) over a wavelength range of 280 to400 nanometers and 2) relatively high light intensity sources such asmedium pressure mercury lamps which provide intensities generallygreater than 10 mW/cm², preferably between 15 and 450 mW/cm². Whereactinic radiation is used to fully or partially polymerize the syruppolymer composition, high intensities and short exposure times arepreferred. For example, an intensity of 600 mW/cm² and an exposure timeof about 1 second may be used successfully. Intensities can range fromabout 0.1 to about 150 mW/cm², preferably from about 0.5 to about 100mW/cm², and more preferably from about 0.5 to about 50 mW/cm². Suchphotoinitiators preferably are present in an amount of from 0.1 to 1.0pbw per 100 pbw of the syrup polymer composition.

Accordingly, relatively thick coatings (e.g., at least about 1 mil or25.4 micrometers) can be achieved when the extinction coefficient of thephotoinitiator is low.

The degree of conversion can be monitored during the irradiation bymeasuring the index of refraction of the polymerizing medium aspreviously described. Useful coating viscosities are achieved withconversions (i.e. the percentage of available monomer polymerized) inthe range of up to 30%, preferably 2-20%, more preferably from 5-15%,and most preferably from 7-12%. The molecular weight (weight average) ofthe solute polymer(s) is at least 100,000, preferably at least 500,000.

When preparing acid functional (meth)acrylate copolymers, it isexpedient for the photoinitiated polymerization reactions to proceed tovirtual completion, i.e., depletion of the monomeric components, attemperatures less than about 70° C. (preferably at 50° C. or less) withreaction times less than 24 hours, preferably less than 12 hours, andmore preferably less than 6 hours. These temperature ranges and reactionrates obviate the need for free radical polymerization inhibitors, whichare often added to acrylic systems to stabilize against undesired,premature polymerization and gelation. Furthermore, the addition ofinhibitors adds extraneous material that will remain with the system andinhibit the desired polymerization of the syrup polymer and formation ofthe crosslinked pressure-sensitive adhesives. Free radicalpolymerization inhibitors are often required at processing temperaturesof 70° C. and higher for reaction periods of more than about 6 to 10hours.

In some embodiments, the acid functional (meth)acrylate copolymers maybe prepared by solution methods. A typical solution polymerizationmethod is carried out by adding the monomers, a suitable solvent, and anoptional chain transfer agent to a reaction vessel, adding a freeradical initiator, purging with nitrogen, and maintaining the reactionvessel at an elevated temperature, typically in the range of about 40 to100° C. until the reaction is completed, typically in about 1 to 20hours, depending upon the batch size and temperature. Examples of thesolvent are methanol, tetrahydrofuran, ethanol, isopropanol, acetone,methyl ethyl ketone, methyl acetate, ethyl acetate, toluene, xylene, andan ethylene glycol alkyl ether. Those solvents can be used alone or asmixtures thereof. The monomer mixture may contain the acyl aziridinecrosslinking agent, or the crosslinking agent may be added to the extantpolymer.

It is preferable to coat the adhesive composition soon afterpreparation. The adhesive polymer composition, (containing thecopolymer, monomers and acylaziridine crosslinking agent), either as asyrup or solution are easily coated upon suitable substrates, such asflexible backing materials, by conventional coating techniques, thenfurther polymerized, and cured or dried, to produce adhesive coatedsheet materials. When emulsion polymerization techniques are used, anemulsion comprising the extant copolymer, acylaziridine crosslinkingagent is coated and dried to produce adhesive coated sheet materials.The flexible backing material may be any material conventionallyutilized as a tape backing, optical film or any other flexible material.

The pressure-sensitive adhesives may also contain one or moreconventional additives. Preferred additives include tackifiers,plasticizers, dyes, antioxidants, and UV stabilizers. Such additives canbe used if they do not affect the superior properties of the emulsionpressure-sensitive adhesives.

If tackifiers are used, then up to about 50% by weight, preferably lessthan 30% by weight, and more preferably less than 5% by weight based onthe dry weight of the total adhesive polymer would be suitable. In someembodiments no tackifiers may be used. Suitable tackifiers for use with(meth)acrylate polymer dispersions include rosin acids, rosin esters,terpene phenolic resins, hydrocarbon resins, and cumarone indene resins.The type and amount of tackifier can affect properties such ascontactability, bonding range, bond strength, heat resistance andspecific adhesion.

Adhesive articles may be prepared by coating the adhesive orpre-adhesive composition of a suitable support, such as a flexiblebacking. Examples of materials that can be included in the flexiblebacking include polyolefins such as polyethylene, polypropylene(including isotactic polypropylene), polystyrene, polyester, polyvinylalcohol, poly(ethylene terephthalate), poly(butylene terephthalate),poly(caprolactam), poly(vinylidene fluoride), polylactides, celluloseacetate, and ethyl cellulose and the like. Commercially availablebacking materials useful in the invention include kraft paper (availablefrom Monadnock Paper, Inc.); cellophane (available from Flexel Corp.);spun-bond poly(ethylene) and poly(propylene), such as Tyvek™ and Typar™(available from DuPont, Inc.); and porous films obtained frompoly(ethylene) and poly(propylene), such as Teslin™ (available from PPGIndustries, Inc.), and Cellguard™ (available from Hoechst-Celanese).

Backings may also be prepared of fabric such as woven fabric formed ofthreads of synthetic or natural materials such as cotton, nylon, rayon,glass, ceramic materials, and the like or nonwoven fabric such as airlaid webs of natural or synthetic fibers or blends of these. The backingmay also be formed of metal, metallized polymer films, or ceramic sheetmaterials may take the form of any article conventionally known to beutilized with pressure-sensitive adhesive compositions such as labels,tapes, signs, covers, marking indicia, and the like.

The above-described compositions are coated on a substrate usingconventional coating techniques modified as appropriate to theparticular substrate. For example, these compositions can be applied toa variety of solid substrates by methods such as roller coating, flowcoating, dip coating, spin coating, spray coating knife coating, and diecoating. These various methods of coating allow the compositions to beplaced on the substrate at variable thicknesses thus allowing a widerrange of use of the compositions. Coating thicknesses may vary aspreviously described. The solutions may be of any desirableconcentration, and degree of conversion, for subsequent coating, but istypically between 20 to 70 wt. % polymer solids, and more typicallybetween 30 and 50 wt. % solids, in solvent. The emulsions also may be ofany desirable concentration for subsequent coating, but is typicallybetween 30 to 70 wt. % polymer solids, and generally contains less than2% unreacted monomer. The syrup polymers may be of any desirableconcentration for subsequent coating, but is typically between 5 to 20wt. % polymer solids in monomer. The desired concentration may beachieved by further dilution of the coating composition, or by partialdrying.

The flexible support may also comprise a release-coated substrate. Suchsubstrates are typically employed when an adhesive transfer tape isprovided. Examples of release-coated substrates are well known in theart and include, by way of example, silicone-coated kraft paper and thelike. Tapes of the invention may also incorporate a low adhesionbacksize (LAB) which are known in the art.

EXAMPLES

Objects and advantages of this invention are further illustrated by thefollowing examples. The particular materials and amounts, as well asother conditions and details, recited in these examples should not beused to unduly limit this invention.

Materials

Abbreviation or Trade Designation Description IOA Isooctyl Acrylate AAAcrylic Acid IBOA Isobornyl Acrylate 2-OA 2-Octyl Acrylate Me-Az2-Methyl Aziridine HDDA 1,6-Hexanediol diacrylate Irgacure 6512,2-dimethoxy-2-phenylacetophenone from CIBA Corporation Tarrytown, NYForal 85 LB Glycerol ester of hydrogenated rosin used as tackifieravailable from Hercules Incorporated, Wilmington, DE Regalrez 6108Hydrocarbon resin used as tackifier available from Eastman ChemicalCompany, Kingsport, TN

Test Methods Peel Adhesion Test [ASTM D 3330/D 3330M-04]

Two 0.5 inch strips of adhesive coated onto Mitsubishi Hostaphan™ primedpolyester film were adhered to a glass plate by rolling a 2 kg rolleronto the tape. The force required to peel the tape at an angle of 180degrees was measured in ounces per 0.5 inches with a platen speed of 90inches per minute. The measurements for the two tape samples wereaveraged. Peel adhesion data was then normalized to Newtons/decimeter(N/dm) for the tables below.

Shear Strength Test [ASTM D-3654/D 3654M 06, PSTC-7]

A 0.5 inch strip of adhesive coated onto Mitsubishi Hostaphan™ primedpolyester film was adhered by its adhesive to a stainless steel (SS)substrate and cut down to leave a 1 in by 0.5 inch sample for 70° C.temperature shear testing. A weight of 2 kg was rolled over the adheredportion. A 500 g load was attached to the tape sample for testing. Eachsample was suspended until failure and/or test terminated. The time tofailure as well as the mode of failure was recorded. Samples were run intriplicate and averaged for the tables below.

Preparation of Acylaziridine Crosslinking Agents

TABLE 1 Acylaziridine Crosslinking Agents ID Number Structure Mol. Wt.(g/mol) I

196 II

183 III

212 IV

255

Preparation of Compound I:N-[1,1-dimethyl-2-(2-methyl-aziridin-1-yl)-2-oxo-ethyl]acrylamide

To a stirred solution of vinyldimethyl azlactone (13.9 g, 0.10 mol,available from 3M Company) in 50 mL of a 30/70 (volume/volume) mixtureof ethyl acetate and hexane was added 2-methylaziridine (7.6 g, about0.12 mol, 90% pure, available from Aldrich) rapidly dropwise. Thereaction mixture was stirred overnight and a white solid was present.The solid was filtered off, washed with 50 mL of hexane, and dried toprovide the desired product (17.4 g). NMR and IR spectral analysesconfirmed the structure of the product.

Preparation of Compound II: Acrylicacid-3-(2-methylaziridin-1-yl)-3-oxopropyl ester

Step 1: Preparation of acrylic acid 2-chlorocarbonyl ethyl ester

To a stirred 0° C. solution of acrylic acid-2-carboxyethyl ester(distilled Aldrich sample, 11.2 g, 78 mmol) in 35 mL of methylenechloride containing 3 drops of dimethylformamide was added dropwise asolution of oxalyl chloride (Alfa, 11.8 g, 93 mmol) in 10 mL ofmethylene chloride. When the addition was complete, the reaction flaskwas removed from the ice bath and the reaction mixture was allowed towarm to room temperature and was stirred overnight. The solvent andexcess oxalyl chloride were then removed at reduced pressure to leave11.6 g of the desired acid chloride as a colorless liquid. NMR and IRspectral analyses confirmed the structure of the product.

Step 2: Preparation of acrylicacid-3-(2-methylaziridin-1-yl)-3-oxopropyl ester

To a stirred 0° C. solution of 2-methylaziridine (5.1 g, about 80 mmol,90% pure, available from Aldrich) and NaOH (3.6 g, 90 mmol) in a mixtureof 50 mL of water and 25 mL of methylene chloride was added dropwise asolution of acrylic acid-2-chlorocarbonylethyl ester (11.6 g, 59 mmol)in 25 mL of methylene chloride. When the addition was complete, thereaction flask was removed from the ice bath and the reaction mixturewas allowed to warm to room temperature and was stirred overnight. Thephases were then separated and the methylene chloride phase was washedonce with 25 mL of water, dried over K₂CO₃, filtered, and solventremoved at reduced pressure to leave 8.1 g of acrylicacid-3-(2-methylaziridin-1yl)-3-oxopropyl ester as a colorless oil. NMRand IR spectral analyses confirmed the structure of the product.

Preparation of Compound III: 2-methylacrylic acid2-[(2-methylaziridine-1-carbonyl)amino ethyl ester

To a stirred 0° C. solution of 2-isocyanatoethyl methacrylate (Aldrich,15.5 g, 0.10 mol) in 100 mL of methylene chloride was added dropwise asolution of 2-methylaziridine (6.3 g, about 0.10 mol, 90% pure,available from Aldrich). When the addition was complete, the reactionflask was removed from the ice bath and the reaction mixture was allowedto warm to room temperature and was stirred overnight. The solvent wasthen removed at reduced pressure to leave 21.0 g of 2-methylacrylic acid2-[(2-methylaziridine-1-carbonyl)aminoethyl ester as a colorless oil.NMR and IR spectral analyses confirmed the structure of the product.

Preparation of Compound IV: 4-(Methylaziridin-1-yl)-4-oxobutyric acid2-acryloyloxy ethyl ester

Step 1: Preparation of acrylic acid 2-(3-chlorocarbonylpropionyloxyethyl ester

To a stirred 0° C. solution of mono(2-acryloyloxyethyl)succinate (TCI,43.2 g, 0.20 mol) in 150 mL of methylene chloride was added dropwise asolution of oxalyl chloride (Alfa, 31.7 g, 0.25 mol) in 50 mL ofmethylene chloride. When the addition was complete, the reaction flaskwas removed from the ice bath and the reaction mixture was allowed towarm to room temperature and was stirred overnight. The solvent andexcess oxalyl chloride were then removed at reduced pressure to leave47.0 g of the desired acid chloride as a colorless liquid. NMR and IRspectral analyses confirmed the structure of the product.

Step 2: Preparation of 4-(Methylaziridin-1-yl)-4-oxobutyric acid2-acryloyloxy ethyl ester

To a stirred 0° C. solution of 2-methylaziridine (14.0 g, about 0.22mol, 90% pure, available from Aldrich) and NaOH (8.8 g, 0.22 mol) in amixture of 70 mL of water and 100 mL of methylene chloride was addeddropwise a solution of acrylic acid 2-(3-chlorocarbonylpropionyloxyethyl ester (46.9 g, 0.20 mol) in 60 mL of methylene chloride. When theaddition was complete, the reaction flask was removed from the ice bathand the reaction mixture was allowed to warm to room temperature and wasstirred overnight. The phases were then separated and the methylenechloride phase was washed once with 50 mL of water and then dried overK₂CO₃ and filtered. The solution was divided into two parts and thesolvent removed from one part at reduced pressure to leave 17.1 g of4-(methylaziridin-1-yl)-4-oxobutyric acid 2-acryloyloxy ethyl ester asyellow oil. NMR and IR spectral analyses confirmed the structure of theproduct. When stored neat, the product was found to somewhat prone topolymerization, and therefore it was stored as the methylene chloridesolution until ready for use.

Examples 2-4 and Comparative C1 and C2 Preparation of the SyrupCopolymer

A one quart jar was charged with 540 g of isooctyl acrylate (IOA, 90parts), 60 g of acrylic acid (AA, 10 parts), and 0.24 g of2,2-dimethoxy-2-phenylacetophenone photoinitiator (Irgacure™ 651, CibaSpecialty Chemicals Inc, 0.04 phr). The monomer mixture was purged withnitrogen for 20 minutes then exposed to low intensity ultravioletradiation until a coatable syrup copolymer was prepared, after which anadditional 0.96 g (0.16 phr) of the photoinitiator was added.

The pre-adhesive polymer syrup was blended with various concentrationsof the acylaziridine crosslinking agent as shown in Table 2. Theformulations were then coated on Mitsubishi Hostaphan™ primed polyesterfilm at a 2 mil (˜50 micrometers) thickness for the syrup pre-adhesiveformulations and cured at 250 mJ/cm². The peel and shear data are shownin Table 2.

For comparative purposes, control examples using no crosslinking agent(Example C1), or using 1,6-hexanedioldiacrylate (using 0.08 phr inExample C2) as the crosslinking agent were also prepared and tested.Peel Adhesion and Shear Strength were measured for tapes prepared fromthese adhesives as described in the test methods above.

TABLE 2 Acylaziridine Compounds 70° C. Shear on SS Shear Peel Adhesionon Example HDDA I III IV 1″ × ½″ × 500 g Avg (min) Failure Mode Glass(N/dm) 90″/min C1 — — — —  16 co 94 C2 0.08 — — —  119 co 89 2A — 0.1 —— 1609 co 73 2B — 0.2 — — 10000+ did not fail 71 2C 0.08  0.05 — — 2062co 71 2D 0.08 0.1 — — 10000+ did not fail 76 3A — — 0.1 — 10000+ did notfail 67 3B — — 0.2 — 10000+ did not fail 66 3C 0.08 —  0.05 — 10000+ didnot fail 72 3D 0.08 — 0.1 — 10000+ did not fail 73 4A — — — 0.1  17 co91 4B — — — 0.2  19 co 94 4C 0.08 — —  0.05 1006 co 92 4D 0.08 — — 0.1 556 co 84 Failure mode legend: (co) stands for cohesive.

Examples 5-7 and Comparative C1 and C2—with Tackifiers

A syrup copolymer was prepared according to the procedure described inExamples 2-4 and Comparative examples C1 and C2.

The pre-adhesive polymer syrup was blended with various concentrationsof the acylaziridine crosslinking agent as well as different amount ofForal 85LB tackifier as shown in Table 3. The formulations were thencoated on Mitsubishi, Hostaphan™ primed polyester film at a 2 mil (˜50micrometers) thickness for the syrup pre-adhesive formulations and curedat 250 mJ/cm². The peel and shear data are shown in Table 3.

TABLE 3 Acylaziridine Compounds 70° C. Shear on SS Shear Peel Adhesionon Example HDDA I III IV Foral 85LB 1″ × ½″ × 500 g Avg (min) FailureMode Glass (N/dm) 90″/min C1 — — — — — 16 co 94 C2 0.08 — — — — 119 co89 5A — 0.1 — — 15 1 co 63 5B — 0.2 — — 15 13 co 61 5C 0.08 0.1 — — 1526 co 53 5D 0.08 0.2 — — 30 0 co 79 6A — — 0.1 — 15 18 co 69 6B — — 0.2— 15 78 po 70 6C 0.08 —  0.05 — 15 29 po 60 6D 0.08 — 0.1 — 30 4 po 437A — — — 0.1 15 0 co 90 7B — — — 0.2 15 0 co 79 7C 0.08 — —  0.05 15 0co 70 7D 0.08 — — 0.1 30 0 co 66 Failure mode legend: (co) stands forcohesive and (po) stands for pop-off.

Examples 8-10 and Comparative C3 and C4 Preparation of the SyrupCopolymer

A one quart jar was charged with 480 g of isooctyl acrylate (IOA, 80parts), 114 g of isobornyl acrylate (IBOA, 19 parts), 6 g of acrylicacid (AA, 1 parts), and 0.24 g of 2,2-dimethoxy-2-phenylacetophenonephotoinitiator (Irgacure™ 651, Ciba Specialty Chemicals Inc, 0.04 phr).The monomer mixture was purged with nitrogen for 20 minutes then exposedto low intensity ultraviolet radiation until a coatable syrup copolymerwas prepared, after which an additional 0.96 g (0.16 phr) of thephotoinitiator was added.

The pre-adhesive polymer syrup was blended with various concentrationsof the acylaziridine crosslinking agent as shown in Table 4. Theformulations were then coated on Mitsubishi Hostaphan™ primed polyesterfilm at a 2 mil (˜50 micrometers) thickness for the syrup pre-adhesiveformulations and cured at 560 mJ/cm². The peel and shear data are shownin Table 4.

For comparative purposes, control examples using no crosslinking agent(Example C3), or using 1,6-hexanedioldiacrylate (using 0.08 phr inExample C4) as the crosslinking agent were also prepared and tested.Peel Adhesion and Shear Strength were measured for tapes prepared fromthese adhesives as described in the test methods above.

TABLE 4 70° C. Peel Adhesion Acylaziridine Shear Shear on GlassCompounds Regalrez on failure (N/dm) Example HDDA I III IV 6108 SS mode90″/min C3 — — — — —   0 co 82 C4 0.08 — — — —  31 co 68 8A — 0.1 — — 153934 co 60 8B — 0.2 — — 15 10000+ Did not 54 fail 8C 0.08  0.05 — — 1510000+ Did not 63 fail 8D 0.08 0.1 — — 30 10000+ Did not 57 fail 9A — —0.1 — 15 10000+ Did not 65 fail 9B — — 0.2 — 15 10000+ Did not 57 fail9C 0.08 —  0.05 — 15 10000+ Did not 63 fail 9D 0.08 0.1 — 30 10000+ Didnot 56 fail 10A — — — 0.1 15   0 co 89 10B — — — 0.2 15   0 co 69 10C0.08 — —  0.05 15  22 co 58 10D 0.08 — — 0.1 30  43 co 51 Failure modelegend: (co) stands for cohesive.

Examples 11-13 and Comparative examples C3 and C4

A syrup copolymer was prepared according to the procedure described inExamples 8-10 and Comparative C3 and C4.

The pre-adhesive polymer syrup was blended with various concentrationsof the acylaziridine crosslinking agent and different amount oftackifier as shown in Table 5. The formulations were then coated onMitsubishi Hostaphan™ primed polyester film at a 2 mil (˜50 micrometers)thickness for the syrup pre-adhesive formulations and cured at 560mJ/cm². The peel and shear data are shown in Table 5.

TABLE 5 70° C. Peel Adhesion Acylaziridine Shear Shear on GlassCompounds Regalrez on failure (N/dm) Example HDDA I III IV 6108 SS mode90″/min C3 — — — — —   0 co 82 C4 0.08 — — — —  31 co 68 11A — 0.1 — —15 3934 co 98 11B — 0.2 — — 15 10000+ Did not 92 fail 11C 0.08  0.05 — —15 10000+ Did not 79 fail 11D 0.08 0.1 — — 30 10000+ Did not 90 fail 12A— — 0.1 — 15 10000+ Did not 100 fail 12B — — 0.2 — 15 10000+ Did not 83fail 12C 0.08 —  0.05 — 15 10000+ Did not 89 fail 12D 0.08 — 0.1 — 3010000+ Did not 104 fail 13A — — — 0.1 15   1 co 84 13B — — — 0.2 15   1co 100 13C 0.08 — —  0.05 15  16 co 92 13D 0.08 — — 0.1 30  35 co 110Failure mode legend: (co) stands for cohesive.

Examples 14 and Comparative Examples C5 and C6

A syrup copolymer was prepared according to the procedure described inExamples 8-10 and Comparative C3 and C4. 2-Octyl acrylate, a monomerderived from renewable sources, was used instead of Isooctyl Acrylate.

The pre-adhesive polymer syrup was blended with various concentrationsof the acylaziridine compound I as crosslinking agent and differentamount of Regalrez 6108 as tackifier (Table 6). The formulations werethen coated on Mitsubishi Hostaphan™ primed polyester film at a 2 mil(˜50 micrometers) thickness for the syrup pre-adhesive formulations andcured at 560 mJ/cm². The peel and shear data are shown in Table 6.

TABLE 6 70° C. Shear Peel Adhesion Acylaziridine Regalrez Shear failureon Glass (N/dm) Example HDDA Compound I 6108 on SS mode 90″/min C5 — — —1 co 79 C6 0.08 — — 61 co, po 68 14A — — 15 0 co 122 14B 0.08 — 15 27 co105 14C — 0.1 15 29 co 114 14D — 0.2 15 9402 co 101 Failure mode legend:(co) stands for cohesive and (po) stands for pop-off.

1. A polymer composition comprising: i. 85 to 99.5 parts by weight ofmonomer units of a (meth)acrylic acid ester of non-tertiary alcohol; ii.0.5 to 15 parts by weight of an acid functional monomer units; iii. 0 to10 parts by weight of a non-acid functional, ethylenically unsaturatedpolar monomer units; iv. 0 to 5 parts vinyl monomer units, v. 0 to 5parts of a multifunctional (meth)acrylate monomer units; and vi. 0.005to 5.0 parts by weight an acylaziridine crosslinking agent of theformula:

wherein R¹ is H or CH₃; X¹ is —O— or —NH—; R² is a divalent alkylene,optionally substituted by one or more catenary ester groups, urea groupsand/or urethane groups, X² is —O— or —NH—; x is 0 or 1; each R³ isindependently —H or a C₁-C₄ alkyl group, and y is 0, 1 or
 2. 2. Thepolymer composition of claim 1 of the formula:

where M_(acrylate) represents polymerized monomer units derived from(meth)acrylate monomers, M_(acid) represents polymerized monomer unitsderived from acid functional monomers, M_(azir) represents polymerizedmonomer units derived from aziridine functional monomers; a, b and c areat least one; R¹ is H or CH₃; X¹ is —O— or —NH—; R² is a divalentalkylene, optionally substituted by one or more catenary ester groups,urea groups and/or urethane groups, X² is —O— or —NH—; x is 0 or 1; y is0, 1 or 2; each R³ is independently —H or a C₁-C₄ alkyl group.
 3. Thepolymer of claim 1 of the formula:

where M_(acrylate) represents polymerized monomer units derived from(meth)acrylic acid ester of non-tertiary alcohol, M_(acid) representspolymerized monomer units derived from acid functional monomers, a and bare at least one; R¹ is H or CH₃; X¹ is —O— or —NH—; R² is a divalentalkylene, optionally substituted by one or more catenary ester groups,urea groups and/or urethane groups, X² is —O— or —NH—; x is 0 or 1; eachR³ is independently —H or a C₁-C₄ alkyl group.
 4. An adhesive articlecomprising a coating of the crosslinked composition of claim 1 on abacking.
 5. The polymer composition of claim 1 comprising 0.05 to 5.0parts by weight of an acylaziridine crosslinking agent, relative to 100parts of the copolymer.
 6. The polymer composition of claim 1 whereinsaid non-acid functional, ethylenically unsaturated polar monomer isselected from 2-hydroxyethyl (meth)acrylate; N-vinylpyrrolidone;N-vinylcaprolactam; acrylamide; t-butyl acrylamide; dimethylamino ethylacrylamide; N-octyl acrylamide; poly(alkoxyalkyl) (meth)acrylates;poly(vinyl methyl ether); and mixtures thereof.
 7. The polymercomposition of claim 1 wherein said copolymer comprises 0.5 to 5 partsby weight of acrylic acid and 1 to 5 parts by weight of a non-acidfunctional, ethylenically unsaturated monomer.
 8. The polymercomposition of claim 1 wherein the acid functional monomer is selectedfrom acrylic acid, methacrylic acid, itaconic acid, fumaric acid,crotonic acid, citraconic acid, maleic acid, oleic acid, β-carboxyethyl(meth)acrylate, 2-sulfoethyl methacrylate, styrene sulfonic acid,2-acrylamido-2-methylpropane sulfonic acid, vinyl phosphonic acid, andmixtures thereof.
 9. The polymer composition of claim 1 comprising 1 to5 parts of a vinyl monomer selected from vinyl esters, styrene,substituted styrene, vinyl halide, vinyl propionate, and mixturesthereof.
 10. The polymer composition of claim 1 with the average numberof carbon atoms of the non-tertiary alcohol being from about 4 to about12.
 11. The polymer composition of claim 1 wherein said non-tertiaryalcohol of said (meth)acrylic acid ester of non-tertiary alcohol isselected from 2-octanol or dihydrocitronellol.
 12. The polymercomposition of claim 1 comprising 90 to 95 parts by weight of monomerunits of a (meth)acrylic acid ester of non-tertiary alcohol.
 13. Thepolymer composition of claim 1 comprising 0.5 to 10 parts by weight ofan acid functional monomer units.
 14. The polymer composition of claim 1comprising 0.5 to 5 parts by weight of a non-acid functional,ethylenically unsaturated polar monomer units.
 15. The polymercomposition of claim 1 comprising: i. 55 to 69.5 parts by weight monomerunits of an (meth)acrylic acid ester of non-tertiary alcohol; ii. 1 to30 parts by weight of monomer units of an (meth)acrylic acid esterhaving a T_(g) of greater than 25° C.; iii. 0.5 to 15 parts by weight ofan acid functional ethylenically unsaturated monomer units; iv. 0 to 10parts by weight of a non-acid functional, ethylenically unsaturatedpolar monomer units; v. 0 to 5 parts vinyl monomer units; and vi. 0 to 5parts of a multifunctional (meth)acrylate units; based on 100 parts byweight total monomer.
 16. The polymer composition of claim 1 comprisingthe reaction product of: a) a copolymer comprising i. 85 to 99.5 partsby weight of monomer units of an (meth)acrylic acid ester ofnon-tertiary alcohol; ii. 0.5 to 15 parts by weight of an acidfunctional monomer units; iii. 0 to 10 parts by weight of a non-acidfunctional, ethylenically unsaturated polar monomer units; iv. 0 to 5parts vinyl monomer units, v. 0 to 5 parts of a multifunctional(meth)acrylate monomer units; and with (b) an acylaziridine crosslinkingagent of the formula:

wherein R¹ is H or CH₃; X¹ is —O— or —NH—; R² is a divalent alkylene,optionally substituted by one or more catenary ester groups, urea groupsand/or urethane groups, X² is —O— or —NH—; x is 0 or 1; each R³ isindependently —H or a C₁-C₄ alkyl group, and y is 0, 1 or
 2. 17. Amethod of preparing a pressure-sensitive adhesive comprising combining;(a) a copolymer comprising i. 85 to 99.5 parts by weight of an(meth)acrylic acid ester of non-tertiary alcohol; ii. 1 to 15 parts byweight of an acid functional monomer; iii. 0 to 10 parts by weight of anon-acid functional, ethylenically unsaturated polar monomer; iv. 0 to 5parts vinyl monomer, v. 0 to 5 parts of a multifunctional (meth)acrylatemonomer units; and with (b) an acylaziridine crosslinking agent of theformula:

wherein R¹ is H or CH₃; X¹ is —O— or —NH—; R² is a divalent alkylene,optionally substituted by one or more catenary ester groups, urea groupsand/or urethane groups, X² is —O— or —NH—; x is 0 or 1; each R³ isindependently —H or a C₁-C₄ alkyl group, and y is 0, 1 or 2; and (c)heating the mixture to effect crosslinking.
 18. An adhesive articlecomprising the crosslinked composition of claim 1 on a backing.